1. Field of the Invention
This invention relates to the field of disk drives and more particularly to an automatic mechanism for loading a read/write head onto and unloading it from a disk surface.
2. Background
Hard disk drives typically use one or more aluminum disks to store computer data. These disks are covered with a magnetic coating that can be selectively magnetized and demagnetized. Data is written to or read from the disk by means of a magnetic read/write head.
During the normal operation, the disks spin at a high rate, typically 3600 rpm. The magnetic read/write heads are positioned in close proximity to the disks but do not contact the disk surfaces. Instead, the heads "float" on a layer of air, called an "air bearing", produced by the aerodynamic action of the spinning disks. This air bearing is very thin. During normal operation, the heads are typically within 10 microinches of the disk surfaces.
Magnetic heads are commonly mounted on a pivoting actuator arm. The actuator arm moves the heads in an arc across the disk surfaces, much like the tone arm of a record player. Since there are no grooves in the magnetic disks to guide the actuator arm, a servo motor is used to pivot the arm. To minimize the amount of energy required to move the arm, the arm must be kept as light as possible. A low arm weight also increases the speed at which the heads can be moved across the disks, and consequently increases the rate at which data head can be positioned over a desired track.
For proper operation of the disk drive, the magnetic heads must not be allowed to contact the disk surfaces. Head disk contact can cause damage to the disk's magnetic coating and a loss of stored data. Physical damage to the magnetic heads may also occur. Damage to a disk or head may make the disk drive inoperative, requiring inconvenient and expensive disassembly and repair.
If a power failure occurs or power to the disk drive is interrupted for any other reason, the disks cease spinning and come to a stop. As the disks stop spinning, the air bearings supporting the magnetic heads dissipate. If the heads are not otherwise supported, they will contact the disk.
Some prior art disk drives have tried to alleviate the effects of a head disk contact by using "parking zones" throughout. A parking zone is an area on the magnetic disk that does not contain any stored data. When power is disconnected to these prior art disk drives, the actuator arm is automatically driven over the parking zone and the heads are allowed to contact the disk as the air bearing dissipates. Because the parking zone does not contain any data, no data is lost because of the head to disk contact. However, physical damage to the heads may still occur and debris may be generated in the drive.
The methods used in these prior art disk drives to move the actuator arm towards the parking zone have adverse effects on the disk drive's cost and performance. In some prior art disk drives the driving mechanism is located directly on the arm. The added weight increases the energy required to move the arm and decreases the speed at which the arm can be moved. In other prior art drives, the residual EMF in the spindle motor coils is used to drive the arm to the parking zone. This method requires complex electronic circuitry that adds to the cost of the disk drive.
The present invention overcomes the limitations of the prior art by providing a means to automatically move the actuator arm to the parking zone without allowing the head to contact the disk, without adding to the weight of the actuator arm, and without requiring complex electronic circuitry.